1. Field of the Invention
The invention relates to an apparatus for increasing the efficiency of multiple downcomer fractional distillation trays. The invention more specifically relates to a process and apparatus providing a higher efficiency multiple downcomer fractionation tray by use of improved antipenetration pans.
2. Related Art
Multiple downcomer fractionation trays were introduced by U.S. Pat. No. 3,410,540 issued to W. Bruckert. This reference describes the characteristic structure and arrangement of the components of a multiple downcomer tray. These include long, narrow, trough-like downcomers spread across the tray with long rectangular areas of tray decking separating the downcomers. The traditional rectangular shape of the downcomers and transverse arrangement of downcomers on vertically adjacent trays is also shown.
Liquid which falls from the bottom of a downcomer of a multiple downcomer tray falls onto the active vapor-liquid contacting area of the next lower tray. It has been recognized in the art that the liquid falling on decking can penetrate the decking, thus bypassing the intended vapor-liquid contacting. U.S. Pat. No. 5,209,875 introduced the use of antipenetration pans suspended between the decking and the downcomer to eliminate this problem. The antipenetration pans are located under the liquid outlets of the upper tray""s downcomer and oriented perpendicular to the downcomers of the lower tray. Liquid exiting the downcomers falls upon the pans and then flows onto the decking of the lower tray.
A more recently developed mounting method for antipenetration pans used on a multiple downcomer style tray is shown in U.S. Pat. No. 6,116,583 issued to J. Agnello. Mechanical details and alternative designs of antipenetration pans are shown in U.S. Pat. No. 5,573,714 to D. R. Monkelbaan et al.
The invention is a novel apparatus designed to increase the overall performance of fractionation columns which contain multiple downcomer fractionation trays. The apparatus comprises a modified antipenetration pan. The antipenetration pan is suspended between vertically adjacent trays, which are mounted transverse to each other. The antipenetration pan intercepts liquid emanating from openings in the bottom of a downcomer of an upper tray and then discharges different portions of the liquid onto the active decking area of the next lower tray at points both under and significantly away from the downcomer openings. This improves the distribution of the liquid on the lower tray. It also retains the antipenetration pans traditional function of preventing the direct passage of liquid through the lower tray.
One broad embodiment of a process employing the invention may be characterized as a fractional distillation process which comprises passing a liquid comprising a first component and a second component onto an upper first tray located in a fractional distillation column containing a plurality of vertically spaced apart fractionation trays operated at fractionation conditions which cause vapor to rise through decking areas provided on the trays while liquid is collected in at least one downcomer forming part of each tray, with liquid which has been collected in a downcomer of the first tray exiting the downcomer through openings located in a lower portion of the downcomer, intercepting liquid, which is passing downward from said openings in the lower portion of the downcomer of the first tray, on a central portion of an antipenetration pan located under said openings and between the first tray and a lower, second tray, with the antipenetration pan also comprising two arms extending away from the central portion and ending at points located at least one-half the width of the central portion away from said central portion and, discharging a portion of the liquid which is intercepted by the central portion of the antipenetration pan onto the decking area of the second tray from each of the two arms of the antipenetration pan.
An apparatus according to the invention may be characterized as an apparatus for performing fractional distillation in a fractionation column, which apparatus comprises an upper first tray and a lower second tray, with both the first and second trays comprising at least one elongated downcomer and two vapor-liquid decking areas adjacent the downcomer, and with the downcomer of the first tray being oriented transverse to the downcomer of the second tray and having at least two groups of liquid outlets in the bottom of the downcomer and, a plurality of antipenetration pans, with the antipenetration pans being mounted at an intermediate level between the downcomers of the first tray and the decking areas of the second tray, and being located under liquid outlets in the bottom of the downcomer of the first tray, the antipenetration pans having a shape which comprises a central portion located under the liquid outlets of the downcomer of the first tray and two extensions aligned parallel with the decking areas of the second tray and reaching over portions of the decking area of the second tray which are not under a group of liquid outlets, whereby at least a first portion of liquid falling from the first tray onto the antipenetration pan is carried to portions of the decking area of the lower second tray which are not under a group of liquid outlets, while a second portion of the falling liquid is allowed to fall from the antipenetration pan onto a portion of the decking area of the second tray which is under the group of liquid outlets. Preferably, only a single antipenetration pan is located under each group of liquid outlets, with a separate antipenetration pan preferably being provided for each group of liquid outlets.